Short definition
Nitrates are nitrogen compounds (NO3⁻) that enter groundwater from fertilizer, manure, septic-field discharge, and atmospheric deposition. EPA’s drinking-water MCL is 10 mg/L as nitrate-nitrogen. Above the MCL, nitrate is a real hazard to infants under 6 months (methemoglobinemia, “blue baby syndrome”) and to pregnant women. Boiling does not remove nitrate — it concentrates it.
What it is
Nitrate is the stable, oxidized form of nitrogen in groundwater. It enters the aquifer from fertilizer applied to fields, manure storage and spreading, septic-system effluent, and (less commonly) atmospheric deposition. Once dissolved, nitrate moves with groundwater and stays in solution. It’s tasteless, odorless, and invisible.
The EPA maximum contaminant level (MCL) for public water systems is 10 mg/L as nitrate-nitrogen (NO3-N), equivalent to about 45 mg/L as the NO3⁻ ion. WA Group A and Group B systems enforce this through WAC 246-290 and 246-291. Private wells are not regulated, but WA Department of Health recommends annual testing for coliform and nitrate on every private well.
The health risk is concentrated on infants under 6 months. Nitrate consumed by an infant is reduced in the gut to nitrite, which oxidizes hemoglobin to methemoglobin — a form that doesn’t carry oxygen. The result is cyanosis (“blue baby”), lethargy, and in severe untreated cases, death. Pregnant women face elevated risk, and chronic high-dose nitrate exposure has been linked in newer research to thyroid effects and some cancers in adults.
Why it matters to a homeowner
Eastern Washington is a known nitrate-impacted region. The Lower Yakima Valley and the Sumas-Blaine Aquifer (Whatcom County) both have documented nitrate impairment, with voluntary Groundwater Management Areas in place. Wells in agricultural counties — Yakima, Franklin, Adams, Grant, parts of Whatcom and Skagit — should be tested for nitrate at minimum every year.
Two things that catch homeowners out:
Boiling concentrates nitrate. It’s the opposite of what intuition says. Boiling drives off water; it leaves the dissolved nitrate behind in higher concentration. A pot of water boiled down by a third has 50% more nitrate per cup than it started with. Boiling is for bacteria, not for nitrate.
A water softener doesn’t remove nitrate. Standard salt-only ion-exchange softeners don’t have the right resin chemistry. The treatments that work are reverse osmosis (point-of-use under-sink) or anion exchange with a nitrate-selective resin (whole-house).
When you’ll encounter this term
- Pregnant household or infants in the home — prioritize nitrate testing on any rural, agricultural, or septic-system well
- Eastern WA agricultural-area home buyer — test as part of due-diligence
- Lawn fertilizer plus a septic system close to a well — increase test frequency
- New well drilled in farming area — test at install and every year regardless of feel or taste
Common variants and disambiguation
- Nitrate (NO3⁻) vs. nitrite (NO2⁻). Different chemistry, both regulated. Nitrite is more acutely toxic at lower levels (MCL 1 mg/L NO2-N). Stable groundwater is usually nitrate; disturbed or anaerobic conditions are sometimes nitrite.
- NO3-N vs. NO3 reporting. Lab results may report either. Convert by a factor of 4.43 (NO3 / NO3-N).
- Nitrate vs. coliform. Different problems, different treatment. Both are routinely tested in private wells.
Common failure modes
- Septic field too close to well. Separation distance violation per WAC. The most common cause of high nitrate in residential rural wells.
- Agricultural runoff into a shallow well. Eastern WA orchard and dairy areas.
- Manure storage adjacent to a well. Common rural cause.
- Ion-exchange softener mistaken for nitrate-removal. Different resin chemistry; salt-only softener does not remove nitrate.
- Boiling for “purity.” Concentrates nitrate (and any other dissolved contaminant).
Cost data
| Item | Cost |
|---|---|
| Mail-in nitrate test (single parameter) | $25–$60 |
| Combined coliform + nitrate panel | $40–$80 |
| Full panel with arsenic, heavy metals | $150–$400 |
| Point-of-use RO under-sink system | $200–$500 hardware + $80–$150 install |
| Whole-house anion-exchange nitrate-removal | $1,500–$3,500 |
| Bottled water for infant formula during testing/treatment lag | $20–$50/week |
What to do if your well tests above 10 mg/L
- Switch to bottled water for any infant under 6 months and any pregnant household member. Don’t wait for a treatment system. Don’t boil — boiling concentrates nitrate.
- Don’t use the well water for infant formula.
- Investigate the source. Septic too close? Fertilizer use upslope? Manure storage? Identifying the contamination route shapes the long-term answer.
- Install treatment. For drinking and cooking only, a point-of-use RO at the kitchen tap is the cheap answer ($200–$500 hardware). For whole-house treatment, anion exchange with nitrate-selective resin ($1,500–$3,500).
- Re-test after treatment. Confirm the system is working.
Washington note
EPA’s MCL of 10 mg/L NO3-N is enforced on WA Group A and B systems via WAC 246-290 / 246-291. The Lower Yakima Valley and the Sumas-Blaine Aquifer are both designated as having documented nitrate impairment, and WA Department of Health and Department of Ecology run voluntary monitoring and outreach programs in those areas.
For private wells: no regulatory mandate, but DOH recommends annual coliform + nitrate testing. Mortgage closings and FHA/VA/USDA loans often require a fresh nitrate test at sale. State-funded testing programs in some agricultural counties periodically offer free or subsidized nitrate testing — check your county health department.
If your well tests in the 5–10 mg/L range (under MCL but elevated), treat it as a watch-list item: re-test every six months, investigate possible sources (septic, fertilizer, manure), and consider preventive treatment if the trend is upward.